REMOTE PRESSURE SENSOR AND METHOD OF OPERATION THEREOF
Pressure sensors, a method of sensing pressure and a method of determining a change in birefringence of a polarization maintaining (PM) optical fiber. In one embodiment, the pressure sensor includes: (1) a source of laser light, (2) a polarization module coupled to the source and configured to modulate a polarization state of the light, (3) a PM optical fiber configured to receive the light into a proximal end thereof and having a sensor coupled to a distal tip of the PM optical fiber and having a pressure-dependent optical anisotropy and (4) a detector configured to receive the light back from the sensor via the proximal end and provide a signal based thereon that indicates a pressure on the sensor.
This application claims the benefit of U.S. Provisional Application Ser. No. 62/133,809, filed by Zhou on Mar. 16, 2015, entitled “Method and Apparatus for Remote Sensing of Pressure,” commonly assigned with this application and incorporated herein by reference.
TECHNICAL FIELDThis application is directed, in general, to pressure sensing and, more specifically, to a remote pressure sensor and a method of operating the same to sense pressure remotely.
BACKGROUNDRemote sensing of pressure is an important function with applications in a wide range of fields, from the oil and gas industry to medical procedures and healthcare. In coronary artery disease treatment, for example, it is often necessary to measure the intravascular blood pressure profile along a diseased vessel region that has significant plaque buildup. Such information about intravascular pressure, and the “fractional flow reserve” derived from it, are important indicators that help guide a clinician's decision on whether certain therapeutic measures, such as stenting, should be taken.
Some conventional pressure sensors are based on piezoelectric material. Piezoelectric sensors are accurate, but they are sensitive to environmental factors, such as temperature change, local stress, and electromagnetic interference. In addition, their construction essentially precludes adapting them to perform additional functions, such as ultrasonic imaging.
Other conventional pressure sensors employ an optical fibers, with a Fabry-Perot etalon coupled to the tip of the fiber. Laser interferometry is used to detect a change in Fabry-Perot cavity length caused by a change in pressure. Unfortunately, optical fiber sensors require a microscopic-scale air cavity which is difficult to fabricate. In addition, detecting the cavity length is complicated, requiring white-light interferometry, and the performance of optical fiber sensors has yet to match the accuracy of the piezoelectric sensors.
SUMMARYOne aspect provides a pressure sensor, a method of sensing pressure and a method of determining a change in birefringence of a polarization maintaining (PM) optical fiber. In one embodiment, the pressure sensor includes: (1) a source of laser light, (2) a polarization module coupled to the source and configured to modulate a polarization state of the light, (3) a PM optical fiber configured to receive the light into a proximal end thereof and having a sensor coupled to a distal tip of the PM optical fiber and having a pressure-dependent optical anisotropy and (4) a detector configured to receive the light back from the sensor via the proximal end and provide a signal based thereon that indicates a pressure on the sensor.
Another embodiment of the pressure sensor includes: (1) a source of laser light of first and second wavelengths, (2) a polarization module coupled to the source and configured to modulate a polarization state of the light, (3) a PM optical fiber configured to receive the light into a proximal end thereof and having a sensor coupled to a distal tip of the PM optical fiber and having a pressure-dependent optical anisotropy, (4) a wavelength-selective coating associated with the sensor and configured substantially to prevent the light of the second wavelength from entering the sensor and (5) a detector configured to: (5a) receive the light of the first wavelength back from the sensor via the proximal end and provide a signal based thereon that indicates the pressure and (5b) receive the light of the second wavelength back from the distal tip via the proximal end and provide a signal based thereon that indicates the birefringence of the PM optical fiber.
Another aspect provides a method of sensing pressure. In one embodiment, the method includes: (1) generating laser light, (2) modulating a polarization state of the light, (3) receiving the light into a proximal end of a PM optical fiber having a sensor coupled to a distal tip thereof, the sensor having a pressure-dependent optical anisotropy, (4) receiving the light back from the sensor via the proximal end and (5) providing a signal based thereon that indicates a pressure on the sensor.
Still another aspect provides a method of reducing an influence of birefringence in a PM optical fiber on a pressure measurement obtained therethrough. In one embodiment, the method includes: (1) generating laser light of first and second wavelengths, (2) modulating a polarization state of the light, (3) receiving the light into a proximal end of the PM optical fiber having an optical sensor coupled to a distal tip thereof, the sensor having a pressure-dependent optical anisotropy, (4) substantially preventing the light of the second wavelength from entering the sensor, (5) receiving the light of the first wavelength back from the sensor via the proximal end, (6) receiving the light of the second wavelength back from the distal tip via the proximal end and (7) providing a signal based on the light that indicates a pressure at the sensor that is substantially independent of a change in a birefringence of the PM optical fiber.
Aspects of the disclosure can be better understood with reference to the following drawings. The components in the drawings are not necessarily to scale, emphasis instead being placed upon clearly illustrating the principles of the present disclosure. Moreover, in the drawings, like reference numerals designate corresponding parts throughout the several views, and in which:
It is realized herein that a need exists for a better remote pressure sensor. More specifically, it is realized herein that a need exists for a remote pressure sensor that is also more robust and reliable but also can accommodate additional functions, such as ultrasonic imaging. Introduced herein are various embodiments of a remote pressure sensor and method of operating the same
Because of the optical axis alignment noted above, the forward propagating light in the PM optical fiber experiences a birefringence from the fiber that directly adds to the birefringence experienced from the EOM 110. However, as light reaches the photoelastic material 223 at the distal tip 209 of the probe 200, the birefringence experienced there cannot be added directly to the birefringences experienced from either the PM optical fiber or the EOM 110. The photoelastic material 223 gains a birefringence that is approximately proportional to the pressure-induced stress it experiences, primarily along the direction of the stress. Referring back to
As noted before, light reflected by the reflective coating 224 traverses the photoelastic material 223 again, propagates back inside the PM optical fiber, towards the proximal end of the probe, and re-enters the console 100. As stated above, the polarization module 105 splits the back-propagating light into two light beams 161, 163. The balanced detector 120 receives the two light beams at its two input ports respectively, and produces an electrical output voltage that is proportional to the difference in the optical power of the two input light beams.
Jones Calculus may be employed to determine how the detector output signal changes as a function of the amount of birefringence experienced at the photoelastic material 223.
φ=2π*Δn*L/λ,
where φ is the (single-pass) birefringent phase shift of the photoelastic material, and λn is the amount of pressure-induced birefringence, measured as a change in refractive index. L is the length of the photoelastic material, and λ is the optical wavelength of laser light in vacuum. As is seen in of
Therefore, a controller 180 in the console can process the detector waveform and derive information about the birefringent phase shift φ, and, in turn, determine the pressure-induced birefringence Δn. Since for a given photoelastic material, the relationship between pressure and Δn is known or can be measured beforehand, the pressure at the distal tip of the probe can be determined from the birefringence measurement above.
Sometimes it is desirable to be able to measure the birefringence of the PM optical fiber in the probe without substantial interference from the sensor in the probe. The embodiments described herein can potentially be calibrated in real-time (during use), to account for and compensate for any deviations of the PM optical fiber from ideal behavior.
Since light of second wavelength is substantially reflected (at least 90%) by the wavelength-selective coating 212, the photoelastic material 223 does not significantly affect its birefringence. Therefore, if the console (100 of
Those skilled in the art to which this application relates will appreciate that other and further additions, deletions, substitutions and modifications may be made to the described embodiments.
Claims
1. A pressure sensor, comprising:
- a source of laser light;
- a polarization module coupled to said source and configured to modulate a polarization state of said light;
- a polarization maintaining (PM) optical fiber configured to receive said light into a proximal end thereof and having a sensor coupled to a distal tip of said PM optical fiber and having a pressure-dependent optical anisotropy; and
- a detector configured to receive said light back from said sensor via said proximal end and provide a signal based thereon that indicates a pressure on said sensor.
2. The pressure sensor as recited in claim 1 wherein said sensor is oriented with respect to said distal tip such that said optical anisotropy lies along an axis that is 45°±5° with respect to a principal axis of said PM optical fiber.
3. The pressure sensor as recited in claim 1 wherein said sensor includes a photoelastic material having a reflective coating configured to reflect at least some of said light incident thereon.
4. The pressure sensor as recited in claim 3 wherein said reflective coating is wavelength-dependent.
5. The pressure sensor as recited in claim 1 wherein said source and said detector are located in a console coupled to said proximal end.
6. The pressure sensor as recited in claim 5 wherein said signal is proportional to a difference between optical powers of light received from said polarization module.
7. A method of sensing pressure, comprising:
- generating laser light;
- modulating a polarization state of said light;
- receiving said light into a proximal end of a polarization maintaining (PM) optical fiber having a sensor coupled to a distal tip thereof, said sensor having a pressure-dependent optical anisotropy;
- receiving said light back from said sensor via said proximal end; and
- providing a signal based thereon that indicates a pressure on said sensor.
8. The method as recited in claim 7 wherein said sensor is oriented with respect to said distal tip such that said optical anisotropy lies along an axis that is 45°±5° with respect to a principal axis of said PM optical fiber.
9. The method as recited in claim 7 wherein said sensor includes a photoelastic material having a reflective coating, said method further comprising reflecting at least some of said light incident on said coating.
10. The method as recited in claim 9 wherein said reflective coating is a wavelength-dependent.
11. The method as recited in claim 7 wherein said generating, said receiving said light back from said proximal end and said providing are carried out in a console coupled to said proximal end.
12. The method as recited in claim 11 wherein said modulation is carried out in a polarization module, and said signal is proportional to a difference between optical powers of light received from said polarization module.
13. A pressure sensor, comprising:
- a source of laser light of first and second wavelengths;
- a polarization module coupled to said source and configured to modulate a polarization of said light;
- a polarization maintaining (PM) optical fiber configured to receive said light into a proximal end thereof and having a sensor coupled to a distal tip of said PM optical fiber and having a pressure-dependent optical anisotropy;
- a wavelength-selective coating associated with said sensor and configured substantially to prevent said light of said second wavelength from entering said sensor; and
- a detector configured to: receive said light of said first wavelength back from said sensor via said proximal end and provide a signal based thereon that indicates said pressure, and receive said light of said second wavelength back from said distal tip via said proximal end and provide a signal based thereon that indicates said birefringence substantially independent of said pressure.
14. The method as recited in claim 13 further comprising a controller configured to cause said polarization module to compensate for said change by adjusting a bias in a said polarization module.
15. The pressure sensor as recited in claim 13 wherein said sensor is oriented with respect to said distal tip such that said optical anisotropy lies along an axis that is 45°±5° with respect to a principal axis of said PM optical fiber.
16. The pressure sensor as recited in claim 13 wherein said sensor includes a photoelastic material having a reflective coating configured to reflect at least some of said light incident thereon.
17. The pressure sensor as recited in claim 16 wherein said reflective coating is a wavelength-dependent.
18. The pressure sensor as recited in claim 13 wherein said source and said detector are located in a console coupled to said proximal end.
19. The pressure sensor as recited in claim 13 wherein said signal is proportional to a difference between optical powers of light received from said polarization module.
20. A reducing an influence of birefringence in a polarization maintaining (PM) optical fiber on a pressure measurement obtained therethrough, comprising:
- generating laser light of first and second wavelengths;
- modulating a polarization state of said light;
- receiving said light into a proximal end of said PM optical fiber having an optical sensor coupled to a distal tip thereof, said sensor having a pressure-dependent optical anisotropy;
- substantially preventing said light of said second wavelength from entering said sensor;
- receiving said light of said first wavelength back from said sensor via said proximal end;
- receiving said light of said second wavelength back from said distal tip via said proximal end; and
- providing a signal based on said light that indicates a pressure at said sensor that is substantially independent of a change in a birefringence of said PM optical fiber.
21. The method as recited in claim 20 further comprising:
- causing said light to pass through a polarization module; and
- compensating for said change by adjusting a bias in a said polarization module.
22. The method as recited in claim 20 wherein said sensor is oriented with respect to said distal tip such that said optical anisotropy lies along an axis that is 45°±5° with respect to a principal axis of said PM optical fiber.
23. The method as recited in claim 20 wherein said sensor includes a photoelastic material having a reflective coating, said method further comprising reflecting at least some of said light incident on said coating.
24. The method as recited in claim 23 wherein said reflective coating is a wavelength-dependent.
25. The method as recited in claim 20 wherein said generating, said receiving said light back from said proximal end and said providing are carried out in a console coupled to said proximal end.
26. The method as recited in claim 20 wherein said modulation is carried out in a polarization module, and said signal is proportional to a difference between optical powers of light received from said polarization module.
Type: Application
Filed: Mar 15, 2016
Publication Date: Sep 22, 2016
Inventor: Gan Zhou (Plano, TX)
Application Number: 15/070,099